Quirks and Quarks

Ancient Indigenous people made durable rock paint from lake goo

The paint for the vivid red petroglyphs at Babine Lake, B.C., has an unusual source

The paint for the vivid red petroglyphs at Babine Lake, B.C., has an unusual source

These vivid red petroglyphs at Babine Lake, B.C., were painted many hundreds, or possibly thousands of years ago with a pigment harvested by ancient Indigenous people from lake goo. (University of Missouri)

Originally published on December 7, 2019.

Detective work by a Canadian anthropologist has revealed the sophistication and creativity of ancient Indigenous artists in B.C. who made pigments for their rock art.

Brandi Lee MacDonald investigated the paint used in the petroglyphs at Babine Lake, about 200 km northwest of Prince George, B.C.  There are more than 150 of these images, which represent a range of animals, human figures, human artifacts like canoes and geometrical patterns.

Researchers haven't yet determined the precise age of the rock art, but people have been in the area for at least 5,000 years. Currently, the Lake Babine Nation inhabits the region, and MacDonald has consulted with them in her work.

The red pigment is characteristic of iron oxide-based paints, often known as ochre pigments, which have been used by people around the world for cave and rock art for up to 200,000 years. However the source for the pigment around Babine Lake wasn't obvious to MacDonald and her team.

The mystery of Lake Babine's red paint

MacDonald analyzed a tiny sample of the paint from a flake collected in the 1970s, so her research caused no damage to the art in place. She used a powerful scanning electron microscope to look at the pigment's microstructure. What the microscope revealed was a surprise.

"We saw all these microtubules, these sort of filament structures which looked totally biological which is not something you see very often in rock art," she told Quirks & Quarks host Bob McDonald.

Electron microscope images of a petroglyph paint sample revealed these tubelike structures which researchers eventually identified as being made by lake bacteria. (MacDonald et al., Scientific Reports)

This began a long search to try and figure out what these tubules were. After consulting colleagues around the world, they eventually identified them as filaments made by bacteria called Leptothrix ochracea

"The paint is bacteria," she said. These bacteria take up iron and silica from the water in which they live to make tubelike filaments in which they live. "So the paint is made of those iron-silicate nanocomposites."

These bacteria inhabit freshwater systems and form colonial microbial mats out of these filaments — which appears to be nothing more than orange-brown lake goo. MacDonald and her team surveyed Babine Lake and in a marshy inlet found samples of the bacterial slime that they think might have been the original source of the raw material for the pigment. 

Producing paint by baking bacteria

"I got very excited and tried to collect some of it," said MacDonald, but that turned out to be more difficult than she anticipated. "As soon as you dip your hands into the water and try to collect some of it, it all dissipates."  Eventually she was able to skim a sample.

The next step was to see if they could produce a nice red pigment from the bacterial slime. The team heated samples and found that below about 600 degree Celsius, the material stayed a dull brownish red. Above 800 degree Celsius it charred to black. But with controlled temperatures of around 700 degree Celsius, the material transformed into a vivid red — the same bright colour as the red of the rock painting.

Samples of the lake bacteria heated to between 600 and 800 degrees (d and e) show vivid colours. Samples heated to lower temperatures (a-c) or higher ones (f) are less impressive (MacDonald et al., Scientific Reports)

There were no signs of kilns or other permanent installations where the material might have been processed around the lake, which leads MacDonald to suspect that the paint was produced by heating the bacterial goo in open hearth fires, carefully watching it until it reached the right temperature. 

It was an impressive feat of innovation and creativity for people who didn't use ceramics or smelt metals, said MacDonald.

"There are researchers in ceramic engineering who are trying to find renewable and non-toxic forms of iron oxide paint," she said. "So what you have engineers trying to reproduce now is something that hunter-gatherers knew how to do a long time ago. It's quite remarkable when you think about it."

MacDonald will be continuing her work at Babine Lake, working with people from the Lake Babine Nation to understand their relationship to artwork better, and also trying to find ways to get accurate dates for when the rock-art might have been produced.

Produced and written by Jim Lebans